The 3rd-Generation Partnership Project (3GPP) is currently standardizing relay nodes for the Long Term Evolution (LTE) radio access technology. From a radio propagation perspective, a relay node is positioned between a base station (called an eNodeB in the LTE standard) and one or more mobile terminals (called user equipment, UE, in the LTE standard). This way, communications between the base station and the mobile terminals are relayed by the relay node.
Specifically, a relay node connects to an associated base station using the same, standard radio link used by ordinary mobile terminals. The relay node then provides radio access to mobile terminals, effectively emulating a base station from the perspective of the mobile terminals, and uses its radio link to the base station as backhaul transport for terminal data.
While relay nodes improve system coverage and capacity, the nodes introduce complexities to the process of propagating system information changes throughout the system. System information includes parameters that describe general information about the system, including the Public Land Mobile Network (PLMN) ID, the system bandwidth, and the like. System information also includes parameters that describe information specific to certain cells in the system, such as the allocation of control channels, paging channel information, cell selection information, and so on.
Known approaches to propagating changes in system information parameters throughout systems that do not support relay nodes effectively ensure that a base station and its associated mobile terminals apply the changes at the same time. In this regard, the base station and terminals are configured to only apply system information changes during or at the start of predefined modification periods that recur periodically. When system information is to be changed, the base station sends a change notification to the terminals over a paging channel. The change notification informs the terminals that the base station will be broadcasting system information changes at the start of the next modification period. When that period eventually starts, the base station broadcasts the changes, and applies the changes itself. The terminals immediately apply the changes upon receipt so that the changes are applied at approximately the same time as when the base station applies them.
Complexities occur in systems that support relay nodes because the relay nodes may not be able to receive the change notification sent by the base station over the paging channel. Moreover, even if relay nodes are able to receive the change notification, the relay nodes may still not be able to receive the actual changes subsequently broadcasted. For example, relay nodes may transmit and receive using the same frequency band. These “in-band” relay nodes are therefore configured to receive transmissions from the base station during certain time slots (i.e., “downlink time slots”), and to transmit to the mobile terminals during other time slots (i.e., “uplink time slots”). If the base station transmits a change notification or actual changes during an uplink time slot, the relay node will not receive that notification or those changes.
Known proposals suggest transmitting system information changes to a relay node over a dedicated channel, so that the relay node can at least receive the changes. However, a problem still remains as to the most appropriate time at which the relay node should apply the changes.